2. Atomic Theory

3. History of Atom Early Greeks believed that matter consisted of tiny particles – they called the “atoms”

5. John Dalton English school teacher in 1800’s Proposed atomic theory

6. Dalton’s Atomic Theory All matter is composed of tiny particles called atoms Atoms of a given element have the same size, mass, and physical properties Atoms cannot be subdivided, created, or destroyed

7. Atoms can combine in simple, whole- number ratios to form compounds In chemical reactions, atoms can combine, separate, or rearrange

9. Dalton’s Theory Today Dalton’s theory still holds true today with a few exceptions Atoms can be subdivided in nuclear reactions Atoms of he same element can have different masses – they are called Isotopes

10. Law of Conservation of Mass Matter and its mass cannot be created or destroyed

12. Law of Definite Composition In a compound, the ratio of atoms is always the same For example: water (H 2 O) always has a mass ratio of 1:8 In water there is always 1 gram of water for 8 grams of oxygen

13. Law of Multiple Proportions Two or more different compounds are composed of the same 2 elements, they are whole number ratios of each other